Systematic and Simulation-Free Coarse-Graining of Polymer Melts Using Soft Potentials

Full atomistic or united atom simulations of multi-chain systems are not feasible at present due to their formidable computational requirements. Molecular simulations with coarse-grained models where each segment represents the center-of-mass of a group of atoms/monomers have to be used instead. While atoms or monomers interact with hard excluded-volume interactions (e.g., the Lennard-Jones potential) and cannot overlap, the coarse-grained segments can certainly overlap and should therefore interact with soft potentials that allow complete particle overlapping. Coarse-grained models, however, reduce the chain conformational entropy, which plays an essential role in the thermodynamic behavior of polymeric systems. In this work we use integral-equation theories and a relative entropy framework for coarse-graining to investigate how the soft potential varies with N (number of segments on each chain) and how well the coarse-grained models can reproduce both structural and thermodynamic properties of the original system. This will provide us with a quantitative basis for choosing small N-values that can still capture the chain conformational entropy, a characteristics of polymers.